1. Field of the Invention
The present invention relates generally to computer-aided methods and systems for manufacturing products in a high volume, automated, continuous process and, more particularly, to improved methods and apparatus for automated retrieval, alignment, placement and securement of singulated bare semiconductor dice within preformed packages for testing and burn-in, followed by optional subsequent removal of the dice from the packages.
2. State of the Art
Integrated circuit devices are well-known in the prior art. Such devices, or so-called xe2x80x9cdice,xe2x80x9d may include a large number of active semiconductor components (such as diodes, transistors) in combination with (e.g., in one or more circuits with) various passive components (such as capacitors, resistors), all residing on a xe2x80x9cchipxe2x80x9d or die of silicon or, less typically, gallium arsenide. The combination of components results in a semiconductor or integrated circuit die which performs one or more specific functions, such as a microprocessor die or a memory die, as exemplified by ROM, PROM, EPROM, EEPROM, DRAM and SRAM.
Such dice are normally designed to be supported or carried in a package having a plurality of externally-accessible pins or leads, to which terminals such as bond pads on the die are electrically connected within the package to access other electronic components employed in combination with the die. A package provides mechanical support and protection for the die, may serve as a heat sink, and is normally square or rectangular in shape. The packages typically comprise a filled polymer compound transfer molded about a die wire-bonded or otherwise electrically connected and physically supported by a lead frame structure, or a two-piece preformed ceramic package to which the die is physically and electrically connected before the package lid is secured. Metal packages are also used, although generally in small quantities and for so-called xe2x80x9cmilitary specxe2x80x9d applications.
Packaging defective dice or unknown bad dice (UBD) which are packaged, tested and then scrapped after proven defective in post-packaging testing is inefficient and costly. Accordingly, the bare dice are often tested for continuity during the die fabrication process and before packaging. Such testing may be and has been accomplished by placing bare die in temporary packages having terminals aligned with the terminals (bond pads) of the die to provide electrical access to the devices on the die and subjecting the die via the assembled package to extensive testing, which includes burn-in and discrete testing. Exemplary state-of-the-art fixtures and temporary packages for die testing are disclosed in U.S. Pat. Nos. 5,367,253 and 5,519,332 (to some of the inventors named herein); U.S. Pat. Nos. 5,448,165; 5,475,317; 5,468,157; 5,468,158; 5,483,174; 5,451,165; 5,479,105; 5,088,190; and 5,073,117. U.S. Pat. Nos. 5,367,253 and 5,519,332, assigned to the assignee of the present application, are each hereby incorporated herein for all purposes by this reference.
Discrete testing includes testing the die devices for speed and for errors which may occur after fabrication and after burn-in. Burn-in testing is conducted at elevated potentials and for a prolonged period of time, typically 24 hours, at varying and reduced and elevated temperatures such as xe2x88x9215xc2x0 C. to 125xc2x0 C. to accelerate failure mechanisms such that die devices which have the potential to prematurely fail during normal operation can be identified and eliminated. Dice which survive discrete testing and burn-in are termed xe2x80x9cknown good die,xe2x80x9d or KGD.
Failure of one die on a multi-chip module (MCM), including a so-called single in-line memory module (SIMM), compromises performance of the entire module or, if identified after assembly but before shipment to the customer, at the least initiates a relatively costly and time-consuming rework process to replace the bad die if the entire MCM is not to be scrapped. Even if individual die yield is relatively high, the combination of such dice in an MCM nonetheless produces an abysmal module yield. For example, if a particular MCM design includes twenty (20) dice with an average xe2x80x9cgood diexe2x80x9d yield rate of 97.3%, the overall yield rate would be predicted to be a dismal 57.3%, which is not commercially viable. Moreover, subjecting the printed circuit or other die carrier of the MCM to burn-in may not be desirable as causing unnecessary stress on elements of the MCM other than the die. Therefore, employing KGD in an MCM is perceived as an optimum way to fabricate high-reliability multi-die products.
However, while desirable, testing bare, unpackaged dice requires a significant amount of handling. The temporary package must not only be compatible with test and burn-in procedures, but must also physically secure and electrically access the die without damaging the die at the bond pads or elsewhere. Similarly, assembly of the die with the package and disassembly after testing must be effected without die damage. The small size of the die itself and minute pitch (spacing) of the bond pads of the die, as well as the fragile nature of the thin bond pads and protective layer covering devices and circuit elements on the active surface of the die, makes a somewhat complex task extremely delicate. Performing these operations at high speeds with requisite accuracy and repeatability has proven beyond the capabilities of the state of the art.
Bond pads are discrete conductive areas on the active face of the die which are used for connecting the internal die circuitry to the conductors of the package. Accurate positioning of the die within the temporary package is therefore critical since alignment of the die bond pads relative to the contacts of the temporary package electrical conductors must be effected in order to subject the die to testing.
Precising die packaging includes mechanically locating a component in a precise position or placement. Various xe2x80x9cprecisingxe2x80x9d methods for this purpose are known in the art. However, there have been several problems associated with such precising methods and systems. For example, it has proven difficult to position the die bond pads in electrical contact with temporary package electrical contacts in an accurate and consistent manner so as to facilitate a repeatable, high volume, continuous assembly process of dice within temporary packages. Another disadvantage associated with prior art equipment and processes is that the die is often destroyed or damaged upon contact with the temporary package, lowering product yield and profit margins. Accurate, repeatable positioning placement and securement of the die in the temporary package is thus critical to providing acceptable KGD qualification on a commercial basis.
One attempt to overcome the problems associated with the prior art has been to precise dice and packages by mechanical fixturing. However, assembly tolerances used in mechanical fixturing techniques are often insufficiently fine to prevent improper alignment. Mechanical fixturing also leads to damage of the die or temporary package. While such techniques have proven useful in improving the accuracy and reliability of the die placement, these techniques do not enable dice to be precisely positioned within temporary packages in a manner that allows production efficiencies capable of supporting large volume operations.
Other systems for alignment and, optionally, placement of various bare and packaged dice are also known in the art. See, for example, U.S. Pat. Nos. 4,526,646; 4,543,659; 4,736,437; 5,052,606; 5,059,559; 5,113,565; 5,123,823; 5,145;099; 5,238,174; 5,288,698; 5,463,227; and 5,471,310 for vision-based systems. A commercially available vision-based aligner bonder for flip chip bonding, offered by Research Devices of Piscataway, N.J., has also been modified by the assignee of the present invention for manual alignment of bare dice with the electrical contacts of a temporary package employed in KGD qualification. It is believed that certain aspects of the commercial Research Devices system may be disclosed in U.S. Pat. No. 4,899,921. A description of the modified Research Devices system appears in the aforementioned U.S. Pat. No. 5,519,332, assigned to the assignee of the present invention and incorporated herein for all purposes by this reference. A discussion of vision systems"" potential applications in the semiconductor industry and associated problems appears in xe2x80x9cA Vision of Vision in the Gigabit Era,xe2x80x9d SEMICONDUCTOR INTERNATIONAL, June 1993, pp. 120-122, 124.
While the foregoing mechanical and visual alignment systems, with ancillary mechanisms for die handling, have achieved some success in their intended applications, to the inventors"" knowledge there exists no fully-automated bare die and package assembly and disassembly system capable of accurate and repeatable operation at a speed making KGD qualification or characterization commercially viable for use as a matter of course in the die fabrication process.
Accordingly, there remains a long-felt need in the semiconductor industry to provide for improved methods and apparatus for assembling dice to be tested with temporary packages (and subsequently disassembling the dice from the packages) in a high volume, cost-efficient and reliable manner. Toward that end, it is essential that the semiconductor or integrated circuit die be positioned and secured within the temporary packages in an automated manner such that die bond pads are aligned with and suitably biased toward temporary package electrical contacts without physical damage to the die structure.
The present invention provides computer-controlled methods and apparatus for automating the positioning of integrated circuit devices or dice within temporary packages utilizing a high volume, continuous process.
Toward that end, the invention provides an automated apparatus for the positioning of bare electronic dice within temporary packages that is used in-line with other machines to facilitate formation of assembled packages which may then be subjected to continuity testing, burn-in and the like.
The invention further includes methods and systems for accurately positioning electronic dice within temporary packages in a reliable, cost-effective manner. Accordingly, the invention provides methods and apparatus for continuous positioning of integrated circuit dice within temporary packages in an automated production sequence while significantly reducing the percentage of dice and temporary package assemblies in which electrical continuity is not established. In so doing, the invention employs multiple inspections of the dice and temporary package prior to, during and after placement of the dice within the temporary package. By inspecting the dice at various stages of assembly, dice which are not properly aligned or positioned can be repositioned to ensure electrical continuity between all of the die bond pads and the contacts of the temporary package electrical conductors. The aforementioned inspections are preferably effected by multiple cameras to facilitate precise placement of the die in the temporary packages in a continuous manner to significantly enhance the efficiency of the assembly process and increase the number of packages in which electrical continuity is established.
In yet another aspect, the invention provides an apparatus for placing dice in temporary packages wherein the packages are supported on carriers (also termed boats or trays) that are conveyed along a path through a predetermined package assembly/disassembly position. A carrier preferably includes a body portion and at least one side rail having a plurality of spaced indexing openings therein. The carrier may be formed of plastic or metal. The conveyor portion of the apparatus further includes an indexing mechanism that functions in conjunction with the indexing openings to place each temporary package in the predetermined assembly/disassembly position to allow the integrated circuit die to be positioned precisely therein.
The invention utilizes previously stored dimensional and visual characteristics for a die as well as similar characteristics of a known temporary package and a known boat or tray to assemble and disassemble electrical dice and temporary packages respectively to and from one another based on predetermined parameters, and to classify the die appropriately.
According to more specific aspects of the present invention, an assembly system is provided to place die bond pads in electrical communication with electrical contacts of temporary package conductors. Once the die bond pads are placed in secure communication with the package contacts, the temporary package can be placed in a standard device tester and subjected to extensive testing. Such testing includes burn-in testing and the like to establish various die characteristics and eliminate mortality in subsequent use of the die. These characteristics, while not meant to be limiting, include the quality of the electrical contact between the die and the temporary package conductors, as well as speed grade characteristics by which the die itself may be classified.
The present invention includes a system which picks up and places a face-up die on a die inverter. The die is then inverted by the inverter and placed in the view field of a rough die camera, which takes a picture of the die. Using positional feedback from the rough die picture, a robot having a primary gripper and also carrying a die restraining device (which may comprise a single or multi-component device) thereon retrieves the die from the inverter. The die is then presented to a fine die camera by the robot and multiple pictures of the die are taken to enhance resolution.
While the die is being located by the die cameras, a carrier (also termed a boat or tray, as previously noted) containing a plurality of temporary package bases is simultaneously indexed to place a temporary package base, located in the carrier, in a predetermined assembly/disassembly position along a conveyor. An electrical socket below the temporary package receives the leads of the temporary package base from below for electrical continuity testing. A rough temporary package picture is then taken of the temporary package base and used to determine a rough location of the temporary package base at the assembly/disassembly position. In a preferred embodiment, a laser height sensor may be used to determine the height of the temporary package base at the assembly/disassembly position prior to taking fine package vision pictures, in order to keep the camera in focus. A fine temporary package camera is then positioned over selected electrical contacts of the temporary package base at the assembly/disassembly position and multiple fine temporary package pictures are also taken to enhance resolution.
The die and die restraining device are then transferred by a primary gripper to the predetermined assembly/disassembly position. The robot aligns the die and temporary package base using the fine temporary package and fine die pictures, and presses the die, die restraining device superimposed on the die, and package together to form an assembled test package which is then tested for continuity using the aforementioned test socket.
During the assembly process, the robot preferably drives the primary gripper carrying the die with the superimposed restraining device downwardly over the package base to a minimum programmed package assembly interlocking height and tests the completed assembly for continuity. If continuity is confirmed, the robot then releases the die restraining device and die. If continuity is not established, the robot increments downward to a maximum programmed force setting. If continuity is still not established, the restraining device and die are removed from the package base. A new package base is placed in the predetermined assembly position and the fine die, rough package, and fine package pictures are retaken. The die with its associated restraining device and the new temporary package base are then assembled and tested.
In an alternative embodiment of the present invention, the robot drives the primary gripper down until physical contact is established between the die and the temporary package. After physical contact is established, the robot drives to a minimum programmed assembly interlocking height. The primary gripper then releases the die and associated lid with the spring and clip of the restraining device and retracts to a waiting position. Electrical continuity of the assembly is tested. If the assembly has electrical continuity between the die and the temporary package base, the process is completed. If electrical continuity is not established, the primary gripper retrieves the die and restraining device and awaits instruction from the operator. The operator may choose to retry assembly of the present temporary package, utilize the next available package base, or purge the die from the system and use the next die.
Any electromechanical device which is capable of transferring component parts from one position to another may be used in the present invention. In a preferred embodiment, however, the transferring device is a robot arm. The apparatus has a control mechanism, including a microprocessor and associated program routines, that selectively controls the robot arm (i) to move the primary gripper to pick up a restraining device and (if lid and other elements of the restraining device such as a spring/clip combination are separate components) to a lid feeder station to pick up a lid, (ii) to move the primary gripper along with the restraining device to pick up the die following photographing by the rough die camera, (iii) to move the primary gripper along with the restraining device and the die to a position to be photographed by the fine die camera, and (iv) to move the restraining device and the die to the predetermined assembly/disassembly position located along the conveyor.
The control routines also function to return the primary gripper to the predetermined assembly position and retrieve the die and restraining device in the event that continuity is not established with the temporary package base. The primary gripper then returns to select a second lid, another restraining device spring/clip element (if separate) and a second die while the carrier is simultaneously indexed to place the next temporary package base of the carrier in the predetermined assembly/disassembly position along the path. The package assembly process continues in this manner.
The present invention, as previously noted, also includes a method and apparatus for disassembling the electrical die and temporary package based on predetermined parameters or characteristics. The disassembly process occurs in a manner substantially opposite the assembly process. In particular, a carrier, boat, or tray containing a plurality of assembled temporary packages containing dice approaches the predetermined assembly/disassembly position. Each package contains a semiconductor die which has been subjected to extensive testing. The primary gripper retrieves the electrical die and restraining device and places it on a die inverter which inverts the face-down die retrieved from the package base to a face-up position. The die is then placed in an appropriate location for further handling, depending upon whether the burn-in and other testing have proven it to be a KGD or a bad die and, if a KGD, of what classification. The lid of the restraining device is released by the primary gripper and a lid precisor similar to the one used for assembly is used to place the lid in a known location.
The foregoing discussion has merely highlighted some of the more pertinent advantages of the present invention. Such advantages should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention as will be described. Accordingly, other advantages and a fuller understanding of the invention may be had by referring to the following detailed description of the preferred embodiments.